Rotation sensor

Abstract

A magnetism detection elements are arranged in an arrangement direction substantially perpendicular to a tooth trace of a gear when viewed from a magnetism generation unit and send a signal according to a magnetic flux flowing between the gear and the magnetism generation unit. A detection unit detects rotation of the gear according to the signal. A case accommodates the magnetism detection elements. A movement restriction unit is equipped to the case and located on the side of the gear at a place between the magnetism detection elements to restrict a magnetic foreign matter, which adheres to the case, from moving in the arrangement direction of the magnetism detection elements.

What is claimed is: 
     
       1. A rotation sensor configured to detect rotation of a gear formed from a metallic material, the rotation sensor comprising:
 a magnetism generation unit equipped to one side in a direction in which a tooth projects from its root of the gear; 
 a plurality of magnetism detection elements arranged in a direction perpendicular to a tooth trace of the gear when being viewed from the magnetism generation unit and configured to send a signal according to a magnetic flux flowing between the gear and the magnetism generation unit; 
 a detection unit configured to detect rotation of the gear according to the signal of the plurality of magnetism detection elements; 
 a case accommodating the plurality of magnetism detection elements; and 
 a movement restriction unit equipped to the case and located on a side of the gear at a place between one of the plurality of magnetism detection elements and an other of the plurality of magnetism detection elements, the movement restriction unit being configured to restrict a magnetic foreign matter, which adheres to the case, from moving in a direction in which the plurality of magnetism detection elements are arranged, wherein 
 the movement restriction unit is a projected portion projected from the case toward the gear and extended in parallel with the tooth trace of the gear, 
 the case and the movement restriction unit are integrally formed from a nonmagnetic material, 
 the plurality of magnetism detection elements include a first magnetism detection element, a second magnetism detection element, and a third magnetism detection element, which are arranged in this order in a direction perpendicular to the tooth trace of the gear, 
 the movement restriction unit is located on a side of the gear relative to the second magnetism detection element, 
 the movement restriction unit has a width in the direction, in which the plurality of magnetism detection elements are arranged, 
 the width of the movement restriction unit is greater than a width of the second magnetism detection element, 
 the width of the movement restriction unit is smaller than a distance between the first magnetism detection element and the third magnetism detection element, and 
 when viewed from the gear, the second magnetism detection element is inside the movement restriction unit. 
 
     
     
       2. The rotation sensor according to  claim 1 , wherein
 the plurality of magnetism detection elements include a first magnetism detection element and a third magnetism detection element, which are arranged in a direction perpendicular to the tooth trace of the gear, and 
 the movement restriction unit is located on a side of the gear at a place between the first magnetism detection element and the third magnetism detection element. 
 
     
     
       3. The rotation sensor according to  claim 1 , wherein
 the movement restriction unit has a length along the tooth trace, and 
 the length of the movement restriction unit is larger than a length of the second magnetism detection element. 
 
     
     
       4. The rotation sensor according to  claim 3 , wherein the length of the movement restriction unit is the same as a diameter of the case. 
     
     
       5. The rotation sensor according to  claim 1 , wherein
 the case accommodates the magnetism generation unit, and 
 the magnetism generation unit is opposed to the gear across the plurality of magnetism detection elements. 
 
     
     
       6. The rotation sensor according to  claim 1 , wherein the gear is configured to direct at least one of teeth of the gear toward the magnetism generation unit in a direction in which the at least one of teeth projects from its root of the gear.